Long-wave or intermediate-frequency transformer



Nov. 1,1921. 1,647372 J. H. PRESSLEY LONG WAVE OR INTERMEDIATE FREQUENCY TRANSFORHER Filed 001' 18. 192

I v I rmzqumcy IN KILOCYCLES 2 W O :0 20 30 4o 50 so 10 e0 gp ilf Ovruzg Patented Nov. 1, 1927.

UNITED STATES JACKSON H. PRESSLEY, OF OCEANIPORT, NEW JERSEY.

LONG-WAVE OR INTERMEDIATE-FREQUENCY TRANSFORMER.

Application filed October 18, 1924. Serial No. 744,376.

My invention relates to electric transformers and has for its object to provide a long wave or intermediate frequency transformer particularly adapted for use in radio I receiving circuits, which object I accomplish as hereinafter described and as illustrated in the accompanying drawings. What I regard as new is set forth in the claims.

The disadvantages of and the difficulty in building a transformer to operate at the incoming radio frequencies lie in the wide band of frequency which must be effectively covered. A transformer-so designed must have such characteristics as to provide practically a constant ratio for all frequencies. To secure satisfactory operation when used in conjunction with an amplifier, the primary winding should have .an impedance several times greater than filament to plate resistance of the vacuum tube with which it is used. This impedance, largely reactive, is due to the inductance of the individual windings and the distributed capacity be-- tween transformer windings. Such conditions promote resonance at certain critical frequencies resulting in good amplification at these points and rather poor amplification at others.

It has been common-practice for radio en gineers to design transformers which are to operate at the incoming signal frequencies with the primary and secondary so adjusted with reference to the turns used and the leakage between primary and secondary, that two resonant circuits,one in the primary and the other in the secondary, are produced. These characteristics produce two resonant frequencies instead of one, with the result that reasonably good amplification is secured over a considerable band of frequency.

In he super-heterodyne method of amplification, a local adjustable oscillator, or generator, is used to produce local oscillations in the antenna circuit differing from the incoming signal frequency by another predetermined frequency. By proper adjustment of the local generator, this difference is kept the same for any signalling frequency. The

signalling frequency and the local impressed frequency interfere to form beats equal to the difference of the two frequencies; These oscillations are then rectified in the output circuit of the rectifier or detector tube. The

beat frequency appears as a true alternating current. This current is then amplified necessity of a special regeneration control and that will function in this way for any type of tube now used in radio receiving sets. I have discovered that these two requirements can be met by a transformer design in which there is negligible leakage between primary and secondary windings,

and to this end I provide a transformer in which the transformer coils are wound in bifilar fashion. Two approximately equal lengths of insulated cop er wire are wound upon a spool side by side and at the same time, the ends of the wires constituting the coils being attached to suitable terminals properly insulated.- Such a transformer has approximately a one to one ratio, and corresponding turns of the primary and secondary are very closely adjacent to each other, being separated by only the insulation of the wire. By winding the coils in this manner, the magnetic leakage is reduced to it minimum.

In the accompanying drawings, which illustrate my improved transformer and the manner in which it is constructed,

Fig. 1 is a perspective view of the complete transformer;

Fi 2 is a. horizontal section on line 2--2 of Fig. 1;

Fig. 3 is a vertical section on line 3-3 of Fig. 2;

Fig. 4: is a perspective view of one of the laminations of which the core is composed;

Fig. 5 is a perspective view illustratin the spool on which t e coils are wound an the manner in which the winding is accomplished;

Fig. 6 is a perspective view of one of the two similar members which together constitute the housing of the transformer; and

Fig. 7 is a curve or graph showing aproximately the characteristics at various requencies of my improved transformer.

My im roved transformer comprises a magnetiza 16 QOI'B 8 of the double loop type composed of a lurality of thin steel laminations 9, prefera ly octagonal in'contour, and each having a transverse centrally-disposed tongue 10, on the opposite sides of which are openings 11, 12, thus giving the double loop formation above mentioned. The tongues 10 of the several laminations, when superposed in the manner illustrated in Fig. 2, together form a central core 13 upon which 1s mount ed a spool 14 lying in the opemn s 11, 12, as shown in Fi 3. Wound upon t e spool 14 in bifilar fas ion aretwo fine insulated co per wires 15, 16 respectively constituting t 1e rimary and secondary coils of the transormer. These wires are of approximately equal length, and are wound upon the spool side by side and at the same time, so that adjacent sections of the windings occupy approximately the same position on the spool, and corresponding turns of the primary and secondary coils are very closely adjacent to each other, being separated only by the insulation of the wire. As shown in Fig. 5, the spool 14is provided with a rectangular central opening or bore 17 to adapt it to fit nicely on the central core 10, and at diametrically opposite sides of said opening it is provided with grooves or recesses 18, 19 to receive terminal wires 20, 21 that are connected with the inner ends of the coil wires 15,16. When the coils have received the required number of turns suitable terminal wires are attached to the outer ends of the coil wires 15, 16, and the several terminal wires are connected to binding osts, as will be hereinafter described. y winding the coils in bifilar fashion as described magnetic leakage is reduced to a minimum.

After the coils have been formed as above described, the spool is mounted upon the central core 10 by threading a suflicient number of laminations 9 into the opening 17 of the spool, after which the core composed of the several laminations is formed into a unitary mass byclamping the laminations together in a housing composed of two complementary members 22, 23 made of insulating material. These members are rectangular in contour, and are provided with triangular corner lugs 24 at their inner faces so that the fit snu ly upon the core, as illustrated in ig. 1. crews 25 extending through the corner portions of the housing members 22, 23 serve to clamp them to ether so that they enclose the core at the si es and at the corners. The housing members 22, 23 are also provided with semi-cylindrical portions 26 which extend over and enclose the projecting portions of'the spool 14 so that the spool is entirely enclosed and protected. At one side of each of the semi-c lindrical portions 26 holes 27, 28 are provi ed for the assage of the terminal wires of the coils, as illustrated in Fig. 1. Binding osts 29, 30 are rovided on the housing mem er 22, and simi ar bind ing posts 31, 32 are provided on the other housin member 23 and to one of these airs of'bin ing posts the terminal. wires 0 the primary coil are connected, while to the other pair the terminal wires of the secondary 0011 are connected. In the illustrated arrangement one of the (primary terminals 20 is shown as connecte to the binding post 29, and the other rimary terminal '33 is shown connected to t e binding post 30. In hke manner the secondary terminal Wire 21 will be connected to the binding post 31 and the other secondary terminal 34 will be connected with binding post 32. The disposition of the several binding posts is, of course, optional, as they may be arranged wherever is most convenient, as for example, if the transformer is desigp'ed to stand on end the binding posts may e placed at the upper end in stea of at the upper side of the housing. The several binding posts are preferably made of metal but are suitably insulated.

The advantages of my im roved trans former are two-fold: First, t e ratio as a function of the applied radio frequencies is more nearly constant than is possible with any other type of winding. This characteristic is illustrated in Fig. 5., Second, wh-n. used in radio frequency receiving sets designed to operate within the range of he quencies indicated, there is less tendency toward regeneration and stability of operation is greatly increased.

What I claim as m invention and to secure by Letters atent is- 1. In an intermediate frequency transformer for superheterodyne receiving sets, the combination of a magnetizable core composed of a pluralit of laminations octagonal in outline, each amination havin a centrall dis osed member having a e end capa le 0 being sprung outwardly from the lamination, a spool having a central opening of rectangular form, the centrally disosed members of said core laminations bemg threaded through the openin in said spool, primary and secondary win mgs both wound simultaneously on said spool in bifilar relation, the rectangular opening in said spool having slots therein through which the inner ends of said'windings are extended to the outside of said spool two housing sections each comprising a iiange portion having laterally projecting lugs adapted to enga e over the slopin corners of said core, an having a semi-0y dricsl portion projecting from said flange ports." for receiving the outer side of said spool, screw means passing through said lu for securing said housing sections over sai cor '1 .and spool, said core having edge portions exposed through openings intervening be tween said lu s, and bin ing posts project ing laterally om each flan portion, the

terminal" ends "of said windings extending up through holes in said semi-cylindrical portions and connecting to said binding posts.

2. In an intermediate frequency transformer for superheterodyne receivers, the combination of a magnetizable core, composed of a plurality of laminations of douhle loop form, each lamination having a centrally disposed member, one end of which is free, a spool having a central opening through which the free ends of said centrally disposed members are threaded, primary and secondary windings both wound simultaneously on said spool in bifilar relation, a housing comprising two complementary housing sections each comprlsing a flange portion having laterally projecting lugs-adapted to engage over the'ed of said core and having semi-cylindrica ortions projecting from said flange portlons for receiving the sides of said spools, screw means passing through said laterally projecting lugs for securing said housing sections together, and binding posts mounted on said housing sections and connected to said primary and secondary windings.

3. An electric transformer comprising a magnetizable core composed of a plurality of laminations shaped to rovide a centrally disposed member, a spool mounted on said member, primary and secondary windings on said spool, and a housing for enclosing said core and spool comprising two complementary housing sections, each having' a flange portion rovided with laterally extending lugs adapted to engage over the edges of said core and having a semi-cylindrical portion adapted to engage over the outer side of said spool, screw means passing through said lugs for securing said housing sections together, and connector terminals mounted on the flange portions of said housing sections.

JACKSON H. PRESSLEY. 

